                The invention relates to a method for testing photovoltaic modules, comprising the following steps:        an AC voltage is modulated onto a photovoltaic module;        the photovoltaic module is scanned using a camera; and        the camera signal produced by the camera is evaluated in order to obtain a luminescence image of the photovoltaic module.        
The invention additionally relates to an apparatus for testing a photovoltaic module, having a device for modulating an AC voltage signal onto the photovoltaic module, having a camera for scanning the photovoltaic module, which camera outputs a camera signal, and having an evaluation device for computing a luminescence image from the camera signal.
Such a method and such an apparatus are known from EP 2 421 052 A2.
According to the known method and the known apparatus, an AC voltage signal is applied to both connections of the photovoltaic module and the modulation is performed both in the forward direction and in the backward direction of the photovoltaic module and the resultant electroluminescence is evaluated. This prompts luminescence images to be captured in the forward direction and in the backward direction and superimposed on one another.
The known method is used for quality control during the manufacture of photovoltaic modules. Like all currently known methods that are based on luminescence, it needs to be performed in a dark room with the exclusion of any sources of illumination, apart from the photovoltaic module itself. In addition, it cannot be used for photovoltaic modules having integral bypass diodes.
J. Coello, “Introducing Electroluminescence Technique as a Quality Control of Large PV Plants” in “26th European Photovoltaic Solar Energy Conference and Exhibition”, pages 3469-3472, 2011, discloses quality control during the manufacture of photovoltaic modules on a large scale by electroluminescence. In this case, the photovoltaic cells have a DC voltage applied to them in the forward direction, so that they radiate in the near infrared range. In this case too, the test is performed in a dark room, without the presence of daylight.
Although such test methods are fundamentally suited to ensuring good quality control during the manufacture of photovoltaic cells, use on already existing photovoltaic modules requires the module in question to be demounted and checked in the dark room.
This means a very high level of outlay and leads to corresponding losses during the checking phase.